How does C/EBPα speed up cell reprogramming?

Much of what is known about how mammalian cells decide what to become derives from the study of transcription factor (TF)-induced transdifferentiation and reprogramming into induced pluripotent stem (iPS) cells. Among the plethora of transdifferentiation systems described1 the C/EBPα-induced conversion of lymphoid progenitors as well as of mature B cells into macrophages is probably the most efficient, reaching 100%.2 This lineage switch does not involve an overt retrodifferentiation into embryonic stem cells (ESCs) or haematopoietic stem cells, but the transient activation of genes specific for granulocyte/macrophage precursors (GMPs)2 (and see below).